Lubricants containing mixed metal salts of mono- and polybasic acids



United States Patent 01 lice 3,339,085 Patented June 18, 1968 3,389,085LUBRICANTS CONTAINING MIXED METAL SALTS F MONO- AND POLYBASEC AClDSArnold J. Morway, Clark, NJ., assignor to Esso Research and EngineeringCompany, a corporation of Delaware No Drawing. Filed Mar. 31, 1964, Ser.No. 356,035 3 Claims. (Cl. 252-41) This invention relates to lubricantscomprising lubricating oil containing alkali metal mixed salts of fattyacids and certain polybasic acid materials, as additives or asthickeners.

In its preferred form, the invention relates to lubricating greasessuitable for lubrication of anti-friction bearings, comprisinglubricating oil thickened with alkali metal mixed salts of monobasicacid, which is preferably a mixture of low molecular weight fatty acidand higher molecular weight fatty acid, and a polybasic acid which canbe phosphoric acid or low molecular weight dicarboxylic acid.

The greases of the invention differ from previously known, relatedalkali metal high temperature bearing greases wherein the thickener is amixed salt of low molecular weight fatty acid, e.g. acetic acid, andhigher molecular weight fatty acid, e.-g. C to C fatty acid. Thus, incontrast to said previously known greases, the greases of the inventiondo not become excessively fluid at elevated temperatures, or becomeexcessively rubbery or fibrous at elevated temperatures, due to phasechanges in the soapthickening structure.

In general, other advantages of the greases of the invention include:anti-wear properties, high dropping points, excellent structuralstability at both low and high rates of shear, good lubrication lives,and in the case of lithium salts, the greases have good waterinsolubility and ability to retain their structural stability when wateris emulsified into the grease.

The mixed-salt systems of the invention are best made to contain alkalimetal salt of 0.05 to 6.0, preferably 0.1 to 4.0 molar hydrogenequivalents of low molecular weight C to C fatty acid per molar hydrogenequivalent of polybasic acid. These systems will usually also containsalt of 0.2 to 3.0, preferably 0.2 to 2 molar hydrogen equivalents ofhigher molecular weight fatty acid, e.g. C to C fatty acid, per molarhydrogen equivalent of said polybasic acid. Greases can be thus preparedhaving a total content of said alkali metal salts of 5.0 to 40.0 weightpercent, preferably to 35 weight percent, based on the total weight ofthe grease. These greases in turn can be diluted with additional oil toform fluid lubricants which have antiwear properties containing about0.1 to 5.0 of the mixed salt.

Suitable low molecular weight fatty acids include C to C fatty acid suchas acetic, propionic, butyric acid, etc. Acetic acid or its anhydride ispreferred.

The higher molecular weight fatty acid includes C to Cnaturally-occurring or synthetic, substituted or unsubstituted,saturated or unsaturated, mixed or unmixed fatty acids. Preferred acidswill have 16 to 24 carbon per molecule. Examples of such acids includemyristic, palmitic, stearic, IZ-hydroxy, stearic, arachidic, oleic,rincinoleic, hydrogenated fish oil, tallow acids, etc.

The low molecular weight polybasic of the invention is selected from thegroup consisting of phosphoric acid which can be either in its ortho,pyro, or meta form, and C to C saturated aliphatic dicarboxylic acidsuch as oxalic, malonic, succinic, glutaric or adipic. The correspondingacid anhydrides, where they exist, can also be used, eg. succinicanhydride.

The alkali metal component of the mixed thickeners is lithium, ormixtures of lithium and sodium.

The lubricating oil used in the compositions of the invention may beeither a mineral lubricating oil or a synthetic lubricating oil.Synthetic lubricating oils which may be used include esters or dibasicacids (eg di-2-ethylhexyl sebacate), ester of glycols (e.g. C Oxo aciddiester of tetraethylene glycol), complex esters (e.g. the complex esterformed by reacting one mole of sebacic acid with two moles oftetraethylene glycol and two moles of 2- ethylhexanoic acid), halocarbonoils, alkyl silicates, sulfite esters, mercaptals, formals, polyglycoltype synthetic oils, etc., or mixtures of any of the above in anyproportions. If the salts are formed in situ in the oil, then this insitu reaction is frequently best carried out in a mineral oil, sincemany synthetic oils will tend to decompose or hydrolyze during the saltformation. However, the salts once formed, can be used in lubricantscontaining the synthetic oils noted above.

Various other additives may also be added to the lubricating composition(e.g. 0.1 to 10.0 weight percent) of detergents such as calciumpetroleum sulfonate; oxidation inhibitors such asphenyl-alpha-naphthylamine; corrosion inhibitors, such as sodium nitriteand sorbitan monooleate; dyes; other grease thickeners, and the like.

The lubricants of the invention can be prepared in a number of differentways. Various specific techniques will be observed in the followingexamples. In general, these techniques involve neutralizing all theacids in at least a portion of the oil, with aqueous alkali metal base,followed by homogenization to remove lumps, then heating to about 300 to550 F., preferably 400 to 500 F. to dehydrate the composition. Thehigher temperature of 400 to 500 F. seems to form some sort of a complexwhich results in the formation of a mixed salt material having greaterthickening effect and better load and BF. properties than the lowerdehydration temperatures. After dehydration, the grease can be cooled,any additives can be added, and the grease can be homogenized again. Ifa lubricating fluid is desired, the grease is simply diluted by mixingwith additional lubricating oil.

The invention Will be further understood by reference to the followingexamples wherein all parts are by weight and wherein stirring wascarried out throughout the grease making procedure in order to obtain amore uniform product.

EXAMPLE I 71.9 parts of a mineral lubricating oil having a viscosity of60 SUS. at 210 F. and 15 parts of Hydrofol Acid 51 were added to afire-heated kettle and heated to 130 F., while stirring, to disperse theacid in the oil. Then, 3 parts of glacial acetic acid were added to thekettle followed by the addition of 6.1 parts of lithium hydroxidemonohydrate (LiOH-H O) in the form of an aqueous solution consisting of20 wt. percent lithium hydroxide results in a faster and more completeneutralization than if dry lithium hydroxide was used. Then the mixturein the kettle was stirred for 15 more minutes, after which 3.0 parts ofoxalic acid (dry) was added to the kettle. Heat was applied to thekettle and the temperature of the kettle contents raised to 210 F.,while stirring. At this point, the wet grease was homogenized by passagefrom the kettle through a Charlotte mill having an opening of 0.010 inchand then returning to the kettle. This homogenization removed all lumpsand specks of salt from the grease and aided in completing thesaponification. The temperature was then increased to 450 F., whichtemperature was maintained for 0.5 hour, to dehydrate the grease andform the desired grease structure. Heating was then discontinued and thegrease was allowed to cool, while stirring to prevent crust formation,until the temperature dropped to 250 F. At this point, one part ofphenyl-alpha-naphthylamine was added as an antioxidant. The grease wasallowed to further cool to F. whereupon it was again homogenized bypassage through the Charlotte mill to form the finished grease.

Hydrofol Acid 51 is a commercial fatty acid made by hydrogenating fishoil and has an average chain length of about 18 carbon atoms and issimilar to stearic acid in its degree of unsaturation.

The homogenizing step while the grease is still in the wet stage, i.e.there is still a lot of water in the grease, is important in obtaining ahomogeneous final product. In the wet stage, the various salts arehydrated and can be smoothed out by homogenization. On the other hand,if the small lumps of salt are not removed by homogenization at thispoint, but instead are heated to high temperatures and dehydrated,subsequent milling will not remove these lumps which have now hardened.The resulting grease would therefore be grainy and give poorerlubrication d-ue to the presence of the hardened lumps. Furthermore, thepresence of these hard lumps reduces the amount of salt available forthickening so as to result in a softer grease due to the poorerutilization of the thickener.

EXAMPLE II This grease was prepared in a manner similar to that of thegrease of Example I except that a different proportion of materials wasused.

EXAMPLE III 15 parts of Hydrofol Acid 51 and 71.9 parts of minerallubricating oil were added to a gas-fired kettle and warmed to 130 F.while mixing to melt the acid into the oil. Then, 4.3 parts of lithiumhydroxide monohydrate were added to the kettle in the form of a 20 wt.percent aqueous solution. Next, 3.0 parts of glacial acetic acid wereadded. The amount of lithium hydroxide monohydrate was just sufiicientto neutralize the Hydrofol Acid 51 and the glacial acetic acid. Thekettle contents were then stirred for /2 hour, after which was added 3parts of oxalic acid crystals (dry) and 1.8 parts of sodium hydroxide(to neutralize the oxalic acid) in the form of a 40% aqueous solution,i.e. 40 wt. percent sodium hydroxide and 60 wt. percent water. Theresulting mixture was then heated to 200 F. and passed through aCharlotte mill having an opening of 0.008 inch and recycling back intothe kettle until all lumps were removed from the grease. The compositionwas then heated to a temperature of about 430 which was maintained forabout 0.5 hour to totally dehydrate the grease. The grease was cooled to250 F., with stirring, where one part of phenyl-alphanaphthylamine wasmixed into the grease. The grease was next cooled with stirring to 120F. and then homogenized by passage through the Charlottle mill to formthe finished grease.

EXAMPLE IV parts of Hydrofol Acid 51 and 76.9 parts of minerallubricating oil was added to a fire-heated kettle and warmed to 130 F.while mixing. 2.9 parts of lithium hydroxide monohydrate in the form ofa 20 wt. percent aqueous solution was then added followed by theaddition of 2 parts of glacial acetic acid. The lithium hydroxide wasused up in neutralizing the Hydrofoil Acid 51 and glacial acetic acid.The resulting mixture was stirred for V2 hour following which 2 parts ofdry oxalic acid crystals and 1.2 parts of sodium hydroxide (toneutralize the oxalic acid and form sodium oxalate) in the form of a 40%aqueous solution were also added. The resulting mixture was then heatedto 200 F., cycled through the Charlotte mill (0.010 inch opening) untilsmooth, dehydrated at 430 to 440 F. for about 0.5 hour, and cooled to250 P. where 1 part of phenyl-alpha-naphthylamine was added, all whilestirring. Then, 4 parts of an oil dispersion consisting of 2 parts offinely divided sodium nitrite as an anti-rust additive and 2 parts ofmineral lubricating oil was added to the grease. The grease was thenhomogenized by again passing through the Charlotte mill to form thefinished grease. The sodium nitrite used above was a commercial gradethat had been ball milled in the mineral oil in a 50/50 weightconcentration.

EXAMPLE V 15 parts of Hydrofol Acid 51 and 70.7 parts of minerallubricating oil were added to a fire-heated kettle and mixed whilegently heating to 130 F. 7.3 parts of lithium hydroxide monohydrate (20%aqueou solution) was added, following which the mixture was stirred for/2 hour. Then, a blend consisting of 3 parts of wt. percentorthophosphoric acid dissolved in 3 parts of glacial acetic acid wasslowly added to the kettle and reacted. This reaction raised thetemperature of the kettle contents to 175 F. The warm grease was thencycled through the Charlottle mill (0.0l0 inch opening) and then back tothe kettle until a smooth homogeneous composition was obtained. Heatingwas then initiated and the temperature of the composition raised to 450F. which temperature was maintained for about 0.5 hour in order to formthe complex salt and totally dehydrate the grease. After this, heatingwas discontinued and the grease cooled to 250 F. while stirring, atwhich point 1 part of phenylalpha-naphthylamine was added. The greasewas then further cooled to F. while stirring, where it was homogenizedin a Morehouse mill to form the finished grease.

EXAMPLE VI A grease was prepared in the same manner as that of Example Vexcept that different proportions of acetic acid and orthophosphoricacid were used.

Composition A A grease was prepared in the same manner as the grease ofExample VI except that no acetic acid was used.

Composition B 76.8 parts of mineral lubricating oil and 15 parts ofHydrofol Acid 51 were added to a fire-heated kettle and stirred whileheating to 130 F. Then 4.3 parts of lithium hydroxide monohydrate in theform of a 20 wt. percent aqueous solution, were added to the mixture,followed immediately by the addition of 3 parts of glacial acetic acid.The composition was then mixed for 30 minutes, after which the wetgrease, which had a temperature of about 140 F., was cycled through aMorehouse mill having an 0.003" opening and then passed back to thekettle until all lumps and small specks had been eliminated. The smooth,wet, milled grease was then heated to a temperature of about 440 R,which was maintained for about 0.5 hour in order to dehydrate themixture. Heating was then discontinued and the grease allowed to cool to250 P. where 1 part of phenyl-alphanaphthylamine was added as anoxidation inhibitor. The grease was then cooled to F., homogenized insaid Morehouse mill to form a finished grease.

Composition C 10 parts of IZ-hydroxy stearic acid was charged to afire-heated kettle along with 87.5 parts of mineral lubricating oil andmixed while heating to F. Then, 1.5 parts of lithium hydroxidemonohydrate was added in the form of a 20 wt. percent aqueous solution.Heating was then initiated and the composition was heated to atemperature of 390 F. which was maintained for about 0.5 hour wherebythe entire composition was dehydrated. The composition was then cooledto 250 R, where 1 part of phenyl-alpha-naphthylamine was added as anoxidation inhibitor. The composition was then cooled to 120 F. and thenhomogenized in a Morehouse mill after which it was packaged.

Composition D 15 parts of Hydrofol Acid 51 and 72 parts of minerallubricating oil was added to the kettle and warmed to 130 F. After this,2.3 parts of lithium hydroxide monohydrate was added in the form of aaqueous solution. This mixture was then stirred for about 0.5 hour inorder to react the lithium hydroxide monohydrate with the Hydrofol Acid51. Next, 3 parts of glacial acetic acid and 3 parts of dry oxalic acidwas added to the 5 composition, followed by the addition of 3.7 parts ofsodium hydroxide in the form of an aqueous solution containing wt.percent NaOH. The last addition neutralized the acetic acid and oxalicacid with the sodium hydroxide. The grease was then heated to 200 F.,cycled through the Charlotte mill until smooth, dehydrated at 10 Theformulations and properties of lubricants of the 20 preceding examplesand compositions are summarized in the following table:

appearance by being smooth and homogeneous. These greases werestructurally stable as illustrated by their small change in penetrationupon working. These greases were water-insoluble and had excellentlubricating properties as illustrated by the Wheel Bearing Test, andtheir long Lubrication Life at elevated temperatures. These results weresurprising since prior attempts to use oxalic acid in grease making havenot been too successful be cause of the inability of obtaining smoothnon-grainy structures, which would have good structural stability. Inaddition, the greases of Examples I and II were tested for temperaturerise in a ball-bearing. In this test, a 204 mm. steel ball bearing ispacked with 3.0 grams of grease, then operated at 10,000 rpm. while itstemperature is measured by thermocouples placed on the outer bearingrace. In this test, using the grease of Example I, the temperatureincreased 20 F. above the room temperature of F. in about twenty minutesand then quickly dropped to a steady state condition of F. This showsthat the grease of Example I was a good channeling grease which quicklyformed a channel for the rapidly rotating steel balls. This channelingproperty TABLE Examples Composition (Wt. percent):

Hydroiol Acid 51. 15.0

Hydroxystearie Acid" Orthophosphoric Acid LiO H'H2O-....

34 1. ac Mole eq. ratio'acetic acid/polybasic acid... lll 1/1 l/l 1/1.5/1 .11/1. Properties:

Appearance Excellent...- Excellent...- Excellent...- Excel1ent ExcellentExcellent. Dropping Point, F 425 400 450 430 450+ 440. ASTM Penetration,77 F. mm./10.

Unworked 200 280 210 204 200 283 Woiked 60 stroke 220 285 215 Worked10,000 strokes 215 310 200 Water Solubility (B oiling water).

Norma I-Iotiman Oxidation, p.s.1. drop in oxygen pressure in 500 hours.

Wheel Bearing Test Slump Leakage, grams Lubigatli on Life, Hours 10,000r.p.m

Insoluble...- llnsolublem. Insolub e Pass....

Pass Pass Pass Pass Pass. 0N8 slump... 10

slump... None. .0 0.0 1.0.

Composition A B C D Composition (Wt. Percent):

Hydroiol Ac d 51 Oxalic Acid Hydroxystearic Acid.--

Orthophosphoric Acid- OH-H Sodium Hydroxide Phenyl-naphthylamine...NaNO; Mineral lubricating oil, 60 SUS. at 210 F Mole eq. ratio-higherfatty acid/polybasic acid.

Mole eq. ratio-acetic acid/polybasic acid -I- Properties:

Appearance Excellent Fair Exccllent...-... Fluldizes and grainy.Dropping Point, F 450 395 340 ASTM Penetration, 77 F. 111111.110:

Uuworked 295 240 190 Worked 60 strokes 315..

Worked 10,000 strokes 358... Water Solubility Insoluble Norma HoflmanOxidation, p.s.i. drop in oxygen] pressure in 500 hours. 2.5 WheelBearing Test:

Slump Pass Leakage, grams None Lubrication Life, Hours 10,000 r.p.m.:

*NLGI-ABE C Spindle Test.

As demonstrated by Examples I and II, and as shown in the precedingtable, greases were made from oxalic acid is important since it reducesthe power consumption which would otherwise be wasted by the churning ofa nonas the polybasic acid, which greases had an excellent 75 channelinggrease. The grease of Example II was also 7 a channeling grease,although not as good as the grease of Example I. Example II showed aninitial temperature rise of 40 F. above the room temperature of 75 F. inabout twenty minutes and then dropped off to a steady state condition of100 F.

Examples III and IV illustrate how good mixed sodiumlithium complexgreases can be prepared using oxalic acid. The good properties of thesegreases were unexpected, since not only is lithium used to make a goodcomplex grease, but the sodium oxalate which is formed is known as awater soluble salt having no grease forming properties of its own. Thegrease of Example IV, which contained sodium nitrite as a rust-inhibitorsuccessfully passed the CRC-L4l Rust Test by showing no rust. Examples Vand VI illustrate the use of orthophosphoric acid as the polybasic acidin forming a good grease.

Compositions A, B, and C represent prior art type of formulations, whileComposition D demonstrates the necessity for coneutralizing all acids atonce when using lithium and sodium bases. Specifically, Composition Ashows that without the acetic acid that the lubricant is not quite asgood with regard to structural stability, i.e. resistance to mechanicalworking, and lubrication life at 300 F. as the greases of the examples.

Composition B shows that without the polybasic acid that the structuralstability was poor. For example, the ASTM penetration increased from 260when worked 60 strokes to 375 mm./ 10 when worked 10,000 strokes thusshowing considerable breakdown in grease structure upon mechanicalWorking.

Composition C shows that without using the acetic acid or low molecularweight polybasic acid, that the grease had a low dropping point.

Composition D shows that upon using the mixed sodium and lithiumcombination, that if the sodium salt of both acetic and oxalic acid isformed, a poor grease results. On the other hand, Examples III and IVshow that by using the sodium only to neutralize the oxalic acid, that agood grease results, thereby demonstrating the desirability of avoidingreacting sodium with the monocarboxylic acids present.

Using some sodium as in Examples III and IV, permits a less expensivegrease which will have good high temperature lubrication life and whichgenerally will not interfere too much with the water insolubility of thegrease as long as most of the metal content of the thickener is lithium.

What is claimed is:

1. A lubricating grease comprising a major amount of mineral lubricatingoil and about 15 to 35 weight percent of lithium salts of acetic acid, Cto C fatty acid, and oxalic acid, wherein the mole equivalent ratio ofsaid acetic acid to said oxalic acid is about 0.1:1 to 4:1, and whereinthe mole equivalent ratio of said C to C fatty acid to said oxalic acidis about 0.2:1 to 2:1.

2. A lubricating grease comprising a major amount of mineral lubricatingoil and about 15 to 35 weight percent of a salt mixture consisting oflithium salts of acetic acid, and C to C fatty acid and sodium salt ofoxalic acid, wherein the mole equivalent ratio of said acetic acid tosaid oxalic acid is about 0.1:1 to 4:1 and wherein the mole equivalentratio of said C to C fatty acid to said oxalic acid is about 0.2:1 to2:1.

3. A method of preparing the lubricating grease of claim 2, whichcomprises neutralizing said acetic acid and said C to C fatty acid withan aqueous solution of lithium hydroxide in at least a portion of saidoil, then adding said oxalic acid and sodium hydroxide in order to formsodium oxalate, then milling the composition to form a homogeneous mass,then dehydrating by heating to 300 to 550 F. and cooling to form saidgrease.

References Cited UNITED STATES PATENTS 2,861,043 11/1958 Morway et al.252-21 2,880,174 3/1959 Morway et a1 252-41 X 2,898,296 8/1959 Pattendenet al 252-41 X 2,908,645 10/1959 Morway 252- 2,923,682 2/1960 Morway252-327 2,967,151 1/1961 Morway 252-18 X 2,988,507 6/1961 Norton et al252-42.1 3,033,787 5/1962 Morway et al 252-59 X 3,214,376 10/1965 Morway252-18 3,223,624 12/1965 Morway et al 252-41 X 3,223,633 12/1965 Morwayet al 252-41 X DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner.

1. A LUBRICATING GREASE COMPRISING A MAJOR AMOUNT OF MINERAL LUBRICATINGOIL AND ABOUT 15 TO 35 WEIGHT PERCENT OF LITHIUM SALTS OF ACETIC ACID,C18 TO C24 FATTY ACID, AND OXALIC ACID, WHEREIN THE MOLE EQUIVALENTRATIO OF SAID ACETIC ACID TO SAID OXALIC ACID IS ABOUT 0.1:1 TO 4:1, ANDWHEREIN THE MOLE EQUIVALENT RATION OF SAID C16 TO C24 FATTY ACID TO SAIDOXALIC ACID IS ABOUT 0.2:1 TO 2:1.